Encoders are used in detecting the position or the angle of a movable component in various mechanical devices. Generally, there are encoders that detect a relative position or angle, and those that detect an absolute position or angle. There are also optical encoders and magnetic encoders. The optical encoders are more affected by foreign substances and the like, and by fluctuations in the amount of detected light.
Patent Literature 1 discloses a technology for achieving a highly noise-resistant and versatile optical encoder capable of accurate movement detections. In this technology, in a detecting optical system, a laser beam output from a light source and with which a scale is irradiated is passed through or is reflected on the scale. A polarization splitting unit then splits the laser beam thus passed through or reflected into polarized components having given polarization directions, and light intensity detecting units detect the respective light intensities of the polarized components thus split.
Patent Literature 2 discloses a technology for enabling an optical encoder to detect an absolute angle within one rotation, without being affected by fluctuations in the amount of detected light caused by some foreign substances or the like. In this technology, ring-shaped signal tracks are provided on an optical scale disk that is rotatably supported and whose rotation angle is to be detected. The signal tracks include polarizers each of which is provided correspondingly to each segment in the circumferential direction of the optical scale disk. The adjacent polarizers have different polarization directions in a rotating direction of the optical scale, and the polarization directions are rotated m/2 times (where m is an integer equal to or more than zero) when the optical scale disk is rotated once.